The AlGaN/GaN-based high electron mobility transistors (HEMTs) are gaining maturity as evidenced from the fact that they have been available from commercial vendors since 2005. The technology development helped to evolve several commercial companies such as those making GaN/AlGaN on Si epiwafers and device makers. Despite the development of commercial epitaxy and device products, research and development still progresses to improve several areas in HEMTs such as epitaxial growth of GaN on 200 mm Si with high breakdown voltage, CMOS compatible processing for HEMTs, and enhancement mode HEMTs processes. One example of development in GaN/AlGaN technology is a project which aims to develop GaN-based normally-off high power switching transistors for efficient power converters. In addition, there are worldwide consortia focusing on the commercialization of GaN products for electronic devices.
As the technology of GaN growth on Si matures, the problems of developing reduced cost silicon compatible device processing is being addressed. The device performance and device cost are mainly determined by process materials, material quality, and various device process steps. The present issues for Si compatible GaN device processes are:
(i) Non-gold based metals are showing good contacts for GaN/AlGaN system, yet as compared to gold-based processes, CMOS-compatible gold-free processes are incompatible with conventional HEMT fabrication.
(ii) No common metal stack is available for source, drain and gate electrodes.
(iii) Source, drain and gate self-align processes using a single mask in a single lithography process step for GaN/AlGaN based HEMTs process are not available.
(iv) Gate, source and drain field plate processes using a single mask is challenging as a result of a need for processing steps to be flexible.
Thus, what is needed is a method for fabrication of HEMTs which which at least partially overcomes the drawbacks of present approaches and provides gold-free CMOS compatible metal stacks for source, drain and gate. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.